A work sheet stocker temporarily stores product work sheets processed by a work sheet processing machine such as a punch press, or the work sheets stored in the work sheet stocker are transported to a next process. In a common work sheet stocker, product work sheets are loaded in a stack from bottom to top in the order in which the product sheets have been processed. However, where the product work sheets are loaded in a stack, it is difficult to take out lower product work sheets in the stack. This affects a setup for the subsequent step. Furthermore, where the product work sheets are formed articles, upper product work sheets in the stack are raised by the formed parts. Consequently, where a large number of work sheets are loaded, the product work sheets may disadvantageously be collapsed. Furthermore, the formed parts of the product work sheets may disadvantageously be crushed or damaged by the weight of the upper product work sheets, the misalignment of the product work sheets stacked in the vertical direction, or the like.
To deal with these problems, the Unexamined Japanese Patent Application Publication (Tokkai-Hei) No. 2006-341969 proposes a work sheet housing system including a work sheet stocker having a shelf with a plurality of stages on each of which a product work sheet is housed. This work sheet housing system enables the product work sheets to be housed in the plurality of stages of the shelf in the work sheet stocker without bringing the product work sheets into contact with one another. The product work sheet in each of the stages can thus be freely taken out. Even if the product work sheets are formed articles, a large number of product work sheets can be housed without being collapsed. The formed parts of the product work sheets are also prevented from being crushed. Furthermore, the Unexamined Japanese Patent Application Publication (Tokkai-Hei) No. 2004-123276 has made a proposal for the problem with the product work sheets that are formed articles.
Where the work sheet stocker having the shelf with the plurality of stages is used as is the case with the work sheet housing system in the Unexamined Japanese Patent Application Publication (Tokkai-Hei) No. 2006-341969, the position of the shelf in the work sheet stocker needs to be switched between a use position where the product work sheets are placed and housed on the shelf and a retract position where the shelf is retracted from the use position. In the Unexamined Japanese Patent Application Publication (Tokkai-Hei) No. 2006-341969, an unloader that houses the product work sheets in the work sheet stocker switches the position of the shelf, allowing required labor to be saved. However, the unloader separately performs an operation of housing the product work sheets in the work sheet stocker and an operation of switching the position of the shelf in the work sheet stocker. Thus, the unloader needs to perform complicated operations in order to house the product work sheet on one stage of the shelf. This is inefficient.